The use of enhanced boiling surfaces, and in particular nucleate boiling surfaces to increase the heat transfer film coefficient on boiling side heat transfer surfaces are well-known.
U.S. Pat. No. 4,769,511 discloses the use of an enhanced nucleate boiling surface to improve the operation of a process for the alkylation of isoparaffins. The use of nucleate boiling surfaces to improve the operation of heat exchange equipment in the reforming of hydrocarbons is disclosed in U.S. Pat. No. 5,091,075.
Enhanced boiling surfaces for use in heat exchange tubes are well known. Applications and details of tube arrangements are further discussed in U.S. Pat. Nos. 3,384,154, 3,821,018, 4,064,914, 4,060,125, 3,906,604, 4,216,826 and 3,454,081. These enhanced boiling surface tubes are made in a variety of different ways which are well known to those skilled in the art. For example, such tubes may comprise annular or spiral cavities extending along the tube surface made by mechanical working of the tube. Alternatively, fins may be provided on the surface. So too, the tubes may be scored to provide ribs, grooves, a porous layer and the like.
U.S. Pat. No. 4,216,826 discloses a heat transfer tube for an exchanger that deforms radial fins to provide annular or spiral cavities around a heat transfer tube that is used for boiling applications.
Generally, the more efficient enhanced tubes are those having a porous layer on the boiling side of the tube which can be provided in a number of different ways well known to those skilled in the art. In one such method, as described in U.S. Pat. No. 4,064,914, the porous boiling layer is bonded to one side of a thermally conductive wall. The porous boiling layer is made of thermally conductive particles bonded together to form interconnected pores.
It is an object of this invention to provide a surface that uses trapped particulate material to provide nucleate boiling sites.
It is a further object of this invention to provide a boiling surface for a heat transfer tube that is readily producible on the inside or outside of heat transfer tubes.
Another object of this invention is to use unbonded particulate material in a boiling surface for a heat transfer tube.